Inspired by a recipe from The New York Times, I’ve adapted this for my own love of bitter marmalade.
For a batch I use 3 sour (Seville) oranges and 1 Meyer lemon, which makes about 5 half-pint jars of marmalade. You can easily triple the quantity and will have no problem. Feel free to switch the ratio of fruit or use other varieties of oranges or lemons.
Well before starting put 5 small plates in the freezer if you don’t have a candy thermometer. See note at end of this recipe.
Cut ends off the citrus fruit until flesh is exposed. Slice in half lengthwise lengthwise, and then cut into ⅛-inch slices, removing seeds as you see them. Cut the pieces in half again or you’ll have long pieces that can be awkward to eat on toast.
Measure the fruit and juice. Place the fruit and an equal amount water in a very large saucepan. The bigger pan will help avoid having a boiled over mess. Boil the fruit and water for 25 minutes. Add as many cups of sugar as you had fruit. (3 cups fruit, 3 cups water and 3 cups sugar, for example). Bring to a boil until a candy thermometer reaches 222º F or use the cold-plate test described below. This will take about 25 to 40 minutes more, but start checking after 20 minutes.Keep an eye on the pot as you do this because it can easily boil up and over if it’s too hot, resulting in a huge sticky mess. Stirring can help reduce the chances of a boil-over, but just keep an eye on things.
When the desired temperature is reached, remove from heat, remove any foam that surfaces. Transfer to jars or let cool a bit longer and store in plastic containers. Keeps refrigerated for 4-5 weeks. Because the jars are not sterilized and processed in a hot-water bath, you must refrigerate this. I suspect you can freeze the jam without any problems. If you process canning jars (half-pint jars for 10 minutes) it can be stored at room temperature until opened.
Note: The Times recipe described a method new to me for testing the jell. Put a bit of the hot jelly on a plate that’s been chilled in the freezer and watch to see if runs down the plate or starts to jell as you tilt the plate. You don’t need a hard jell for this test to indicate it’s ready.